• Unlike plants, humans have organs which are specialised for the removal of certain excretory products
• They include the?lungs and kidneys
• The?liver?also has a vital role in excretion

Organs involved in excretion

• Excretion is the?removal of the waste substances of metabolic reactions (the chemical reactions that take place inside cells), toxic materials and substances in excess of requirements
• Carbon dioxide?must be excreted as it dissolves in water easily to form an acidic solution which can?lower the pH of cells
• This can?reduce the activity of enzymes?in the body which are essential for controlling the rate of metabolic reactions
• For this reason, too much carbon dioxide in the body is?toxic
• Urea?is also toxic to the body in higher concentrations and so must be excreted

The urinary system in humans

Main structures involved: